Invertebrate Animals

Phylum Porifera

Example: sponges

Invertebrate

Multicellular

Mostly marine, some freshwater

A sponge consists of an outer layer of covering cells, an inner layer of flagellated cells, and some cells in between. Water moves in through many small pores, and out through one large pore. Nutrients and oxygen are absorbed directly from the water into the cells.

Each body segment has a pair of jointed limbs that may be used for swimming, crawling or feeding.

Bilateral symmetry

2 pairs of antennae

1 pair of jaws

Heart and blood vessels

Gills

Straight digestive tract with separate mouth and anus

Simple brain and sensory organs

Sexual reproduction, usually with separate sexes

CLASS MYRIAPODA

Examples: centipede, millipede

Invertebrate, ventral nerve cord

Bilateral symmetry

1 pair of antennae

Brain and sensory organs of eyes, feelers and skin

Air tubes called tracheae for breathing

Heart and blood vessels

Straight digestive tract with separate mouth and anus

Sexual reproduction, with separate sexes

This group is sometimes divided into two classes - Class Chilopoda (Centipedes) and Class Diplopoda (Millipedes).

Did You Know That...? Centipedes do not have 100 legs, nor do millipedes have 1000 legs. In fact, a centipede has 1 pair of legs per body segment, and a millipede has 2 pairs of legs per body segment. Another difference is that centipedes are carnivorous and can be poisonous, and millipedes are herbivorous.

Did You Know That...? Spiders don't get caught in their own webs because they produce two types of web threads - non-sticky threads which provide structure for the web and on which the spider crawls, and sticky threads to catch the prey.

Sexual reproduction - Some insects such as bees produce offspring by parthenogenesis also. Many insects produce chemicals called pheromones to attract mates.

Many insects, e.g. bees, ants and termites, live in organised social groups.

Did You Know That...? Only female mosquitoes suck blood. Male mosquitoes have a deeper hum than the shriller female hum. They make the humming sound by vibrating their wings.

Phylum Echinodermata

Examples: starfish, sea cucumber, sea urchin, sand dollar

Invertebrate

Radial symmetry

Marine

"Spiny skin"

Mouth surrounded by 5 arms with tube feet that move by a hydraulic system

Internal structure made of calcium carbonate

Well-developed digestive system

Simple nervous and circulatory systems

Sexual or asexual reproduction

Echinoderms are thought to be the invertebrate group that most closely resembles the chordate group because there are similarities between the larval stage of the echinoderms and some of the simpler chordates called the acorn worms.